Roller clutches are installed between inner and outer coaxial clutch races so as to create a one way braking action between the races. The main structural component of the roller clutch is a cage, which is basically a ring of interconnected, four sided pockets, each of which pockets contains a roller and its associated energizing spring. Increasingly, such cages are molded of plastic, for weight and cost reasons. A familiar problem to designers of molded plastic roller clutch cages is the differential rate of expansion and contraction that exists between the plastics typically used and the races themselves, which are machined from steel. Specifically, with rising temperatures, the cage tends to expand more than the outer race, binding into it and potentially buckling in compression. With falling temperatures, the cage tends to contract more than the inner race, binding around it in tension. A certain amount of "give" in the cage to allow it to accommodate these differential temperature effects without excessive cage compression or tension is desirable.
Several known methods for building give into the cage are disclosed in older U.S. patents. In co assigned U.S. Pat. No. 4,045,192 to Johnson, each roller pocket is a separately molded piece that is snapped to the next with a joint that has some looseness or "rattle" built into it. Each pocket can move freely back and forth, at least within the limits of the joints, allowing the cage to shrink or grow freely to prevent excess tension or compression. However, a multi piece cage is the most expensive to manufacture and assemble, and a one piece cage is much preferred.
The plastic cage shown in the now expired U.S. Pat. No. 4,570,762 to Husmann takes the different approach of a cage which, while not totally one piece, has only two unitary side rails 4 and 5 which snap together to form a plurality of pockets. The side rails are provided not with loose or rattling joints, but with what are supposed to be flexible are shaped elements 26 and 27 molded into the side rails 4 and 5 at several points. The are shaped elements 26 and 27 are arrayed in radially opposed pairs, opening away from one another. Even though the side rails 4 and 5 are as radially wide as they can possibly be, that is, nearly as wide as the radial space between the clutch races, the elements 26 and 27 are limited in depth to less than half the side rail's radial thickness. And since the arms of the U shaped elements 26 and 27 are so limited in length, they are inevitably stiffer than they would be if they could be made longer. More important, since the side rails 4 and 5 must support the load between the races (the cage has no journal blocks as such), the elements 26 and 27 cannot be made too flexible without inevitably weakening the side rails 4 and 5, in which they are clearly the weakest link. More significant, the Husmarm approach would be impossible in anything but a cage design with full radial width side rails. Today, cage side rails are far more likely to have an "over-under" design in which each side rail is half that radial width or less, in order to allow the cage to be molded in one piece with only two molds.
Another basic approach is to cut relief slots through the cage at various points around it's circumference, which slots open in alternating axial directions, usually one slot for each pocket. The slots create alternating hinge points about which the pockets can flex or bend relative to one another, effectively allowing the cage to give as it shrinks or expands. However, such slots may cut completely through the cage pocket side rails, as in co assigned U.S. Pat. No. 4,712,661 to Lederman, weakening the side rails even more than in the Husmann patent discussed above and destroying the structural completeness of the roller pockets. In an improved version of the basic slot design shown in co assigned U.S. Pat. No. 4,830,157 to Lederman, structurally complete, four sided roller pockets are provided, but at the expense of cutting slots through the journal blocks so that one of the roller pocket cross bars 38 can run through the slot. This inevitably weakens the journal block, which is no longer radially solid. Any slotted cage also suffers from the drawback that the various pockets tip or skew relative to one another about the alternating hinge points left by the slots, and, if an odd number of pockets and slots exists, the skewing action can lead to cage distortion.
The latest design that allows for an even, non distorting cage "give", while still providing structurally complete, four sided roller pockets, is shown in co assigned U.S. Pat. No. 4,850,463 to Lederman. The design takes a different approach to providing "give" in the cage circumference, with no yield points molded into the side rails and no slots cut into the cage. Each cage pocket is four sided and complete, but one cross bar 18 in each pocket is deliberately made thinner in order to be relatively flexible. Each flexible cross bar 18 is then connected to a stiff cross bar 20 of the adjacent pocket by an inflexible and centrally located connector 22. When the cage shrinks or expands, the stress is concentrated by the connectors 22 at the centers of the thin cross bars 18, which bow in or out at the center to provide the necessary give. The flexure is evenly and symmetrically distributed. However, prior to installation, the roller pockets can skew or tip relative to one another about the single, centrally located connector. Also, only the heavier cross bars 20 on one side of each roller pocket are thick and strong enough to act as so called journal blocks to keep the races coaxial and transfer loads. Ideally, all roller pockets would be bordered by two thick (and inflexible) cross bars that were able to provide load support between the races. Providing that ideal case and yet still providing the necessary flex and give in the cage to accommodate temperature effects, without cage distortion prior to installation, remains an unmet design challenge.